1. Field of the Invention
This invention relates generally to electroporation, and more particularly to systems and methods for treating BPH tissue sites of a patient using electroporation.
2. Description of the Related Art
Electroporation is defined as the phenomenon that makes cell membranes permeable by exposing them to certain electric pulses (Weaver, J. C. and Y. A. Chizmadzhev, Theory of electroporation: a review. Bioelectrochem. Bioenerg., 1996. 41: p. 135-60). The permeabilization of the membrane can be reversible or irreversible as a function of the electrical parameters used. In reversible electroporation the cell membrane reseals a certain time after the pulses cease and the cell survives. In irreversible electroporation the cell membrane does not reseal and the cell lyses. (Dev, S. B., Rabussay, D. P., Widera, G., Hofmann, G. A., Medical applications of electroporation, IEEE Transactions of Plasma Science, Vol 28 No 1, February 2000, pp 206-223).
Dielectric breakdown of the cell membrane due to an induced electric field, irreversible electroporation, was first observed in the early 1970s (Neumann, E. and K. Rosenheck, Permeability changes induced by electric impulses in vesicular membranes. J. Membrane Biol., 1972. 10: p. 279-290; Crowley, J. M., Electrical breakdown of biomolecular lipid membranes as an electromechanical instability. Biophysical Journal, 1973. 13: p. 711-724; Zimmermann, U., J. Vienken, and G. Pilwat, Dielectric breakdown of cell membranes. Biophysical Journal, 1974. 14(11): p. 881-899). The ability of the membrane to reseal, reversible electroporation, was discovered separately during the late 1970s (Kinosita Jr, K. and T. Y. Tsong, Hemolysis of human erythrocytes by a transient electric field. Proc. Natl. Acad. Sci. USA, 1977. 74(5): p. 1923-1927; Baker, P. F. and D. E. Knight, Calcium-dependent exocytosis in bovine adrenal medullary cells with leaky plasma membranes. Nature, 1978. 276: p. 620-622; Gauger, B. and F. W. Bentrup, A Study of Dielectric Membrane Breakdown in the Fucus Egg. J. Membrane Biol., 1979. 48(3): p. 249-264).
The mechanism of electroporation is not yet fully understood. It is thought that the electrical field changes the electrochemical potential around a cell membrane and induces instabilities in the polarized cell membrane lipid bilayer. The unstable membrane then alters its shape forming aqueous pathways that possibly are nano-scale pores through the membrane, hence the term “electroporation” (Chang, D. C., et al., Guide to Electroporation and Electrofusion. 1992, San Diego, Calif.: Academic Press, Inc.). Mass transfer can now occur through these channels under electrochemical control. Whatever the mechanism through which the cell membrane becomes permeabilized, electroporation has become an important method for enhanced mass transfer across the cell membrane.
The first important application of the cell membrane permeabilizing properties of electroporation is due to Neumann (Neumann, E., et al., Gene transfer into mouse lyoma cells by electroporation in high electric fields. J. EMBO, 1982. 1: p. 841-5). He has shown that by applying reversible electroporation to cells it is possible to sufficiently permeabilize the cell membrane so that genes, which are macromolecules that normally are too large to enter cells, can after electroporation enter the cell. Using reversible electroporation electrical parameters is crucial to the success of the procedure, since the goal of the procedure is to have a viable cell that incorporates the gene.
Following this discovery electroporation became commonly used to reversible permeabilize the cell membrane for various applications in medicine and biotechnology to introduce into cells or to extract from cells chemical species that normally do not pass, or have difficulty passing across the cell membrane, from small molecules such as fluorescent dyes, drugs and radioactive tracers to high molecular weight molecules such as antibodies, enzymes, nucleic acids, HMW dextrans and DNA.
Following work on cells outside the body, reversible electroporation began to be used for permeabilization of cells in tissue. Heller, R., R. Gilbert, and M. J. Jaroszeski, Clinical applications of electrochemotherapy. Advanced drug delivery reviews, 1999. 35: p. 119-129. Tissue electroporation is now becoming an increasingly popular minimally invasive surgical technique for introducing small drugs and macromolecules into cells in specific areas of the body. This technique is accomplished by injecting drugs or macromolecules into the affected area and placing electrodes into or around the targeted tissue to generate reversible permeabilizing electric field in the tissue, thereby introducing the drugs or macromolecules into the cells of the affected area (Mir, L. M., Therapeutic perspectives of in vivo cell electropermeabilization. Bioelectrochemistry, 2001. 53: p. 1-10).
The use of electroporation to ablate undesirable tissue was introduced by Okino and Mohri in 1987 and Mir et al. in 1991. They have recognized that there are drugs for treatment of cancer, such as bleomycin and cys-platinum, which are very effective in ablation of cancer cells but have difficulties penetrating the cell membrane. Furthermore, some of these drugs, such as bleomycin, have the ability to selectively affect cancerous cells which reproduce without affecting normal cells that do not reproduce. Okino and Mori and Mir et al. separately discovered that combining the electric pulses with an impermeant anticancer drug greatly enhanced the effectiveness of the treatment with that drug (Okino, M. and H. Mohri, Effects of a high-voltage electrical impulse and an anticancer drug on in vivo growing tumors. Japanese Journal of Cancer Research, 1987. 78(12): p. 1319-21; Mir, L. M., et al., Electrochemotherapy potentiation of antitumour effect of bleomycin by local electric pulses. European Journal of Cancer, 1991. 27: p. 68-72). Mir et al. soon followed with clinical trials that have shown promising results and coined the treatment electrochemotherapy (Mir, L. M., et al., Electrochemotherapy, a novel antitumor treatment: first clinical trial. C. R. Acad. Sci., 1991. Ser. III 313(613-8)).
Currently, the primary therapeutic in vivo applications of electroporation are antitumor electrochemotherapy (ECT), which combines a cytotoxic nonpermeant drug with permeabilizing electric pulses and electrogenetherapy (EGT) as a form of non-viral gene therapy, and transdermal drug delivery (Mir, L. M., Therapeutic perspectives of in vivo cell electropermeabilization. Bioelectrochemistry, 2001. 53: p. 1-10). The studies on electrochemotherapy and electrogenetherapy have been recently summarized in several publications (Jaroszeski, M. J., et al., In vivo gene delivery by electroporation. Advanced applications of electrochemistry, 1999. 35: p. 131-137; Heller, R., R. Gilbert, and M. J. Jaroszeski, Clinical applications of electrochemotherapy. Advanced drug delivery reviews, 1999. 35: p. 119-129; Mir, L. M., Therapeutic perspectives of in vivo cell electropermeabilization. Bioelectrochemistry, 2001. 53: p. 1-10; Davalos, R. V., Real Time Imaging for Molecular Medicine through electrical Impedance Tomography of Electroporation, in Mechanical Engineering. 2002, University of California at Berkeley: Berkeley. p. 237). A recent article summarized the results from clinical trials performed in five cancer research centers. Basal cell carcinoma, malignant melanoma, adenocarcinoma and head and neck squamous cell carcinoma were treated for a total of 291 tumors (Mir, L. M., et al., Effective treatment of cutaneous and subcutaneous malignant tumours by electrochemotherapy. British Journal of Cancer, 1998. 77(12): p. 2336-2342).
Electrochemotherapy is a promising minimally invasive surgical technique to locally ablate tissue and treat tumors regardless of their histological type with minimal adverse side effects and a high response rate (Dev, S. B., et al., Medical Applications of Electroporation. IEEE Transactions on Plasma Science, 2000. 28(1): p. 206-223; Heller, R., R. Gilbert, and M. J. Jaroszeski, Clinical applications of electrochemotherapy. Advanced drug delivery reviews, 1999. 35: p. 119-129). Electrochemotherapy, which is performed through the insertion of electrodes into the undesirable tissue, the injection of cytotoxic dugs in the tissue and the application of reversible electroporation parameters, benefits from the ease of application of both high temperature treatment therapies and non-selective chemical therapies and results in outcomes comparable of both high temperature therapies and non-selective chemical therapies.
Irreversible electroporation, the application of electrical pulses which induce irreversible electroporation in cells is also considered for tissue ablation (Davalos, R. V., Real Time Imaging for Molecular Medicine through electrical Impedance Tomography of Electroporation, in Mechanical Engineering. 2002, PhD Thesis, University of California at Berkeley: Berkeley, Davalos, R., L. Mir, Rubinsky B., “Tissue ablation with irreversible electroporation” in print February 2005 Annals of Biomedical Eng,). Irreversible electroporation has the potential for becoming and important minimally invasive surgical technique. However, when used deep in the body, as opposed to the outer surface or in the vicinity of the outer surface of the body, it has a drawback that is typical to all minimally invasive surgical techniques that occur deep in the body, it cannot be closely monitored and controlled. In order for irreversible electroporation to become a routine technique in tissue ablation, it needs to be controllable with immediate feedback. This is necessary to ensure that the targeted areas have been appropriately treated without affecting the surrounding tissue. This invention provides a solution to this problem in the form of medical imaging.
Medical imaging has become an essential aspect of minimally and non-invasive surgery since it was introduced in the early 1980's by the group of Onik and Rubinsky (G. Onik, C. Cooper, H. I. Goldenberg, A. A. Moss, B. Rubinsky, and M. Christianson, “Ultrasonic Characteristics of Frozen Liver,” Cryobiology, 21, pp. 321-328, 1984, J. C. Gilbert, G. M. Onik, W Haddick, and B. Rubinsky, “The Use of Ultrasound Imaging for Monitoring Cryosurgery,” Proceedings 6th Annual Conference, IEEE Engineering in Medicine and Biology, 107-112, 1984 G. Onik, J. Gilbert, W. K. Haddick, R. A. Filly, P. W. Collen, B. Rubinsky, and L. Farrel, “Sonographic Monitoring of Hepatic Cryosurgery, Experimental Animal Model,” American J. of Roentgenology, May 1985, pp. 1043-1047.) Medical imaging involves the production of a map of various physical properties of tissue, which the imaging technique uses to generate a distribution. For example, in using x-rays a map of the x-ray absorption characteristics of various tissues is produced, in ultrasound a map of the pressure wave reflection characteristics of the tissue is produced, in magnetic resonance imaging a map of proton density is produced, in light imaging a map of either photon scattering or absorption characteristics of tissue is produced, in electrical impedance tomography or induction impedance tomography or microwave tomography a map of electrical impedance is produced.
Minimally invasive surgery involves causing desirable changes in tissue, by minimally invasive means. Often minimally invasive surgery is used for the ablation of certain undesirable tissues by various means. For instance in cryosurgery the undesirable tissue is frozen, in radio-frequency ablation, focused ultrasound, electrical and micro-waves hyperthermia tissue is heated, in alcohol ablation proteins are denaturized, in laser ablation photons are delivered to elevate the energy of electrons. In order for imaging to detect and monitor the effects of minimally invasive surgery, these should produce changes in the physical properties that the imaging technique monitors.
The formation of nanopores in the cell membrane has the effect of changing the electrical impedance properties of the cell (Huang, Y, Rubinsky, B., “Micro-electroporation: improving the efficiency and understanding of electrical permeabilization of cells” Biomedical Microdevices, Vo 3, 145-150, 2000. (Discussed in “Nature Biotechnology” Vol 18. pp 368, April 2000), B. Rubinsky, Y Huang. “Controlled electroporation and mass transfer across cell membranes U.S. Pat. No. 6,300,108, Oct. 9, 2001).
Thereafter, electrical impedance tomography was developed, which is an imaging technique that maps the electrical properties of tissue. This concept was proven with experimental and analytical studies (Davalos, R. V., Rubinsky, B., Otten, D. M., “A feasibility study for electrical impedance tomography as a means to monitor tissue electroporation in molecular medicine” IEEE Trans of Biomedical Engineering. Vol. 49, No. 4 pp 400-404, 2002, B. Rubinsky, Y. Huang. “Electrical Impedance Tomography to control electroporation” U.S. Pat. No. 6,387,671, May 14, 2002.)
There is a need for improved systems and methods for treating BPH using electroporation.